Rigid gas permeable (RGP) lenses are manufactured from materials that exhibit a high degree of polarity, resulting in a strong interaction with proteins and other tear constituents that ultimately produce tenacious surface deposits. Current state of the art care systems combat this problem through the use of unpreserved abrasive cleaners that produce microscopic scratches which, in time, shorten the useful life of the lens. Some attempts have been made to competitively block surface deposition by so-called "conditioning" solutions, but this approach involves the use of cytotoxic preservatives and does not eliminate the need for the abrasive cleaner.
Proteolytic enzymes have been of marginal value in controlling surface deposition because their action is limited to proteinaceous material. Multifunctional esterases capable of lysing both proteins and lipids failed to significantly improve on the results obtained with their proteolytic counterparts and the consequences of their usage was a delayed, but persistent, surface deposition and premature loss of the lens.
Aside from the problem of ultimate surface contamination, the RGP lens wearer is also faced with an initial discomfort problem until the lens completely hydrates, at which time it displays its best wetting and consequently its greatest comfort. In order to ensure that this maximal comfort is maintained, it is essential that the wettability of the surface be maintained. Moreover, the capability of the lens to resist surface deposition is also directly related to the maintenance of its wettability. The current state of the art lens care systems do not maintain optimal wettability over long periods of time because they are passive systems formulated to deal with the result of the polymer's surface interactions rather than to eliminate its cause.
RGP lenses have the potential of providing an unsurpassed level of comfort for a rigid lens. Unfortunately, the wearer realizes this benefit for only a short period of time because the current passive RGP care systems are unable to maintain this property.
Initial treatment of new RGP lenses usually includes cleaning with an abrasive cleaner, after which the lens may be soaked in a viscous, polar solution, to purportedly interact with active sites on the lens surface and thereby block their interaction with contaminants. The failure of this system to achieve this result is evident in the fact that the abrasive cleaner must be used on a daily basis and even then, adjunctive products are frequently needed. "Conditioning" then must require abrading the surface as part of the process. Aside from the lack of efficacy of this system, it shortens the functional life of the lens thereby producing a financial loss for the wearer.
Known and/or FDA approved cleaning and wetting solutions for RGP contact lenses utilize hydrophobic preservatives or disinfecting agents such as benzalkonium chloride or chlorhexidine. These hydrophobic materials tend to reduce the wettability of RGP lenses, especially fluorinated RGP lenses, thereby making cleaning and wetting more difficult. A surfactant polymer may be added to such formulations specifically to attempt to overcome the effect of the hydrophobic preservative.
A need exists for an active RGP lens care system that deals with the causes of surface deposition and poor wetting without resorting to the use of abrasives, cytotoxic chemicals or enzymes, and without the use of preservatives that reduce the wettability of the lenses.
A need also exists for a new preservative system for contact lens solutions.